The present invention relates to fluorosilicone compositions and more particularly the present invention relates to the production of fluorosilicone polymers by the polymerization of fluoro-substituted cyclic polysiloxanes in the presence of certain select chain-stoppers.
The processes for producing diorganopolysiloxane polymers and more specifically high molecular weight diorganopolysiloxane polymers are well known. In the case of alkyl and aryl substituted polymers, the process comprises taking the appropriate diorganodichlorosilane and hydrolyzing it. The hydrolyzate that is obtained is then taken and most of the acid and water removed from it. The hydrolyzate is then taken and there is added to it an alkali metal hydroxide. The mixture is then heated at elevated temperatures for sufficient periods of time, so as to preferentially distill the desired cyclic polysiloxanes. Although such a procedure, which is known as a cracking process, produces cyclic polysiloxanes in which the repeating SiO unit varies from 3 to 10 times, most of the cyclic polysiloxanes are cyclotrisiloxane or cyclotetrasiloxane. Further the cracking procedure can be carried out such that the majority of the cyclic polysiloxanes that are formed are either cyclotetrasiloxanes or cyclotrisiloxanes.
When it is desired to produce a diorganopolysiloxane polymer having methyl and phenyl substituents it is desirable to form as much of the cyclo tetrasiloxanes as can be formed. Then the cyclotetrasiloxanes are taken in relatively pure form and there is added to them small amounts of a basic equilibration catalyst and the appropriate amount of chain-stoppers and the mixture of ingredients is heated at elevated temperatures for a period of time so as to produce high molecular weight diorganopolysiloxane polymers, that is polymers having a viscosity of anywhere from 500,000 to 300,000,000 centipoise at 25.degree. C. and more preferably polymers having a viscosity varying from 1,000,000 to 300,000,000 centipoise at 25.degree. C. After the polymerization has reached its highest level the mixture is cooled down, there is added to it a neutralizing ingredient so as to neutralize the basic catalyst and the excess cyclics are removed so as to yield the desired diorganopolysiloxane polymer. It should be noted that such a procedure is traditionally used to make high molecular weight diorganopolysiloxane polymers. However, it can be utilized to produce low molecular weight diorganopolysiloxane polymers such as those having a viscosity of 500,000 to 1,000,000 centipoise at 25.degree. C.
It should be noted that what determines the molecular weight of the final diorganopolysiloxane polymer that is formed during the polymerization reaction is the amount of chain-stopper that is present in the reaction mixture. Such chain-stoppers are usually triorganosiloxy end-stopped diorganopolysiloxane polymers of low molecular weight such as disiloxanes, trisiloxanes and so forth. An example of a suitable chain-stopper for such processes is for instance hexamethyldisiloxane.
The amount of such chain-stoppers in the reaction mixture determines the amount of chain-stoppers available to terminate the polymers that are formed from the cyclo polysiloxane and accordingly, this determines the final molecular weight of the diorganopolysiloxane polymer. As can be appreciated, the smaller the relative amount of the chain-stopper, the higher the molecular weight of the final polymer and the more of the chain-stopper there is present the lower the molecular weight of the final polymer. It should be noted that one procedure for making silanol terminated diorganopolysiloxane polymers in the molecular weight range of 1,000 to 100,000 centipoise viscosity at 25.degree. C. or more, is to take the appropriate low molecular weight silanol material as a chain-stopper and add the desirable amount of such chain-stopper in a mixture of the desired cyclotetrasiloxanes with the appropriate amount of acid or basic equilibration catalyst, and equilibrate the mixture to produce the desired polymer. It is undesirable to have any such low molecular weight silanol terminated diorganopolysiloxane polymer as a chain-stopped for the production of high viscosity diorganopolysiloxane polymers since the presence of silanol groups in such polymers prior to the cure of the composition in the presence of filler results in excessive structuring of the composition such that it can become essentially useless. Accordingly, the presence of silanol groups or moisture is undesirable in the preparation of high viscosity diorganopolysiloxane polymers for the heat vulcanizable silicone rubber compositions, where the organo groups in such diorganopolysiloxane polymers are selected from alkyl groups and aryl groups such as methyl and phenyl.
Accordingly, it was unexpected that silanol groups could be beneficially introduced into a high molecular weight diorganopolysiloxane polymer containing fluorinated substituent groups. However, with respect to the production of fluorinated substituted diorganopolysiloxane polymers it is necessary to discuss the traditional production of such polymers. Triorganosiloxy end-stopped fluorinated substituted high viscosity diorganopolysiloxane polymers are produced by first taking the appropriate fluoro-substituted diorganodichlorosilanes and hydrolyzing them. The hydrolyzate is then taken and its acidity reduced to the appropriate level and the hydrolyzate is separated from excess water. Then there is added to the purified hydrolyzate the appropriate amount of alkali metal hydroxide catalyst and the hydrolyzate is heated at temperatures of about 200.degree. C. or more so as to preferentially distill overhead fluorinated substituted cyclo trisiloxanes. In fluorosilicone chemistry it has been found that cyclo trisiloxanes react more readily in forming polymers than do the corresponding cyclotetrasiloxanes. Accordingly, there is taken the appropriately formed fluorinated substituted cyclo trisiloxanes and there is added to them a basic polymerization catalyst with the appropriate amount of triorganosiloxy end-stopped low molecular weight polymers and the resulting mixture is heated at elevated temperatures so as to form the desired diorganopolysiloxane polymer. However it has been found out that such fluorinated cyclo trisiloxanes polymerize quickly to form the desired high or low molecular weight polymer, so that the traditional low molecular weight triorganosiloxy end-stopped diorganopolysiloxane chain-stoppers whether fluorinated or not do not enter into the cyclo trisiloxane reaction mixture quickly enough. It has been found that such traditional chain-stoppers take from 4 to 6 hours to react appropriately into the cyclo trisiloxane reaction mixture so as to form the desired molecular weight diorganopolysiloxane polymers. Without the slowness of the low molecular weight triorganosiloxy end-stopped chain-stoppers either a low viscosity or a high viscosity fluorinated substituted diorganopolysiloxane polymer could be formed within an hour by the equilibration reaction of the fluorinated substituted cyclo trisiloxane. Thus if the chain-stoppers could react faster into the fluorinated substituted cyclo trisiloxane reaction mixture a high viscosity polymer having a viscosity of 500,000 to 300,000,000 centipoise at 25.degree. C. or preferably having a viscosity of varying from 1,000,000 to 300,000,000 centipoise at 25.degree. C. could be produced as short a time as 1 hour equilibration time. Accordingly, it was highly desirable to find appropriate chain-stoppers for the polymerization of fluorinated substituted cyclo trisiloxanes such that a high viscosity polymer having a viscosity varying from 500,000 to 300,000,000 centipoise at 25.degree. C. could be produced in as short a period of time as 1 hour. This would result in a more efficient and economical process for the production of fluorinated substituted silicone polymers and in turn in the production of fluorinated substituted silicone elastomeric compositions. In this respect it was desirable that any chain-stopper that was selected for such a process produced a polymer that had as good physical properties as the fluorinated substituted polymers produced by the prior art processes.
Accordingly, it is one object of the present invention to provide for a low molecular weight silanol terminated polymer as a chain-stopper for fluorinated substituted cyclo siloxanes so that fluorinated substituted diorganopolysiloxane polymers could be produced more efficiently and more economically.
It is another object of the present invention to provide for a high molecular weight alcohol as a chain-stopper in the equilibration of fluorinated substituted diorganopolysiloxane polymers so as to provide for more efficient and economic process for producing such polymers.
It is an additional object of the present invention to provide for a process for producing high molecular weight fluorinated substituted diorganopolysiloxane polymers in which the process is more efficient and economic than prior art processes and in which the final polymer has properties which are as good as the fluorinated substituted diorganopolysiloxane polymers produced by prior art processes. These and other objects of the present invention are accomplished by means of the disclosures set forth herein below.